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This work systematically investigates the influence of InAs growth conditions and superlattice parameters on the optical properties of InAs/GaAs quantum dot (QD) superlattice structures grown by molecular beam epitaxy. Using surface photovoltage spectroscopy, one directly obtains the absorption spectra up to the highest confined QD levels at room temperature. Based on photoluminescence measurements at different excitation wavelengths, a feature below the fundamental transition is attributed to the transition from uncoupled dots in the bottom layers. The QD transition energy shift was found to be correlated with material intermixing, driven by enhanced strain strength with the increase of layer number and the decrease of spacer thickness, and the growth rate of InAs. A blueshift observed in low growth rate samples is indicative of greatly enhanced intermixing. For QD superlattices grown at a relatively high deposition rate of InAs, the material intermixing effect is gradually enhanced with increasing layer numbers, which will compensate the electronically coupled effect and will prevent further energy shift toward the lower energy side. The absorption wavelengths in 10- and 30-period InAs/GaAs QD superlattices with higher growth rates are near 1.32 μm. The results suggest that these QD superlattice structures can be used as promising active media for long-wavelength QD lasers operating at room temperature. [ABSTRACT FROM AUTHOR]

The authors report on midinfrared photoreflectance measurements of the band gap (E0) and spin-orbit splitting energies (Δ0) in InAs-rich InAsSb and GaInAsPSb samples for varying antimony contents ≤22.5%. The E0 behavior as a function of Sb content is consistent with the literature value bowing parameter of ∼670 meV. However, Δ0 does not exhibit the positive bowing of +1170 meV quoted in the literature: rather, a best fit to their data tentatively suggests a negative bowing of -225 meV. This result is likely to have strong impact due to the importance of the Δ0 parameter in governing InAsSb-based device performance [ABSTRACT FROM AUTHOR]

Detailed studies are reported on the photoluminescence of InAsSb/InAs multiple quantum wells grown by molecular beam epitaxy on InAs substrates with the Sb mole fraction ranging from 0.06 to 0.13. From 4 K photoluminescence the band alignment was determined to be staggered type II. By comparing the emission peak energies with a transition energy calculation it was found that both the conduction and valence bands of InAsSb alloy exhibit some bowing. The bowing parameters were determined to be in the ratio of 4:6. For a sample with Sb composition ∼0.12 in the quantum well the photoluminescence emission band covers the CO2 absorption peak making it suitable for use in sources for CO2 detection. [ABSTRACT FROM AUTHOR]

We report the effects of In[SUB0.33]Ga[SUB0.67]As capping layers on the structural and optical properties of InAs self-organized quantum dots grown by gas-source molecular-beam epitaxy. With different deposition methods for the InGaAs capping layer, the quantum-dot density can be adjusted from 2.3 × 10[SUP10] to 1.7 × 10[SUP11]cm[SUP-2]. As-cleaved 3.98-mm-long diode laser using triple stacks of InAs quantum dots with the capping layer grown by GaAs/InAs sequential binary growth demonstrates an emission wavelength of 1305 nm and a threshold current density of 360 A/cm[SUP2]. A ground-state saturation gain of 16.6 cm[SUP-1] is achieved due to the high dot density. [ABSTRACT FROM AUTHOR]